1. Field of the Invention
The present invention relates to a marking method and apparatus which use relief-plate printing.
2. Prior Art
In conventional marking devices, as shown in FIG. 4, a printing plate 50 is attached to a plate holder 51, and the plate holder 51 is mounted to a pivotal lever 53 via screw 54. The pivotal lever 53 pivots up and down by a cam 52. A spring 55 pulls the lever 53 towards the cam 52 so that the lever 53 steadily follows the surface of the cam 52. Reference numeral 56 is a workpiece upon which printing is performed. The workpiece 56 is positioned and carried on a workpiece carrying table 57.
In this prior art apparatus, since the plate holder 51 is driven up and down via the cam 52, the distance the printing plate 50 is lowered is fixed. If the thickness or height of the workpiece 50 is different, the press-in distance of the printing plate 50 into the workpiece is not consistent from workpiece to workpiece. As a result, the thickness of the printed characters differs, and uniform printed characters cannot be obtained.